1. Field of the Invention
The present invention relates to the modification of optical properties of a surface, and, more particularly, to ion etching of the surface with chemically active ions.
2. Description of Related Art
The optical properties of a surface can be modified by fabricating micro structures into the surface. These structures are useful in the fields of optical gratings, crossed grating structures, and binary optics.
Current etching technology for optical surfaces depends upon the removal of material from the substrate by kinetic bombardment. The kinetic energy of the incoming ion, typically a noble gas such as argon, is transferred to the substrate at the point of impact, causing substrate molecules to break off.
However, the prior art approach suffers from two disadvantages. The first relates to the presence of accumulated debris in the etched areas, and the second relates to control of depth and shape of the etched areas.
With regard to accumulated debris, the removed material can fall back into the etched structures, like debris falling into a meteor crater, or it can deposit onto the sidewalls of etched grooves. This debris prevents the etching of highly defined or deep structures that are vital to tailoring the properties of an optical surfaces.
With regard to control of depth and shape of the etched areas, the kinetic energy of the ions by the prior art process is varied by adjusting the anode voltage. However, this method of control does not have sufficient precision.
Thus, there remains a need for an etching process to modify the surface for the formation of precision optical gratings, crossed grating structures, and binary optics.